1. Field of the Invention
The present invention relates to a system for measuring a distance to an object to be measured and more particularly to an active distance measurement system favorably applied to various types of cameras.
2. Related Background Art
Such an active distance measurement system applied to cameras generally includes an infrared-emitting diode (IRED) for emitting an infrared beam toward an object to be measured, and a position sensitive detector (PSD) for receiving the object-reflected infrared beam. The signal output from the PSD is a signal responsive to a position where the object-reflected infrared beam is received. A signal processing and arithmetic unit determines a distance to the object to be measured from this signal. Because a large error may occur at once measurement, averaging of multiple pieces of distance information is generally performed to obtain more accurate distance information.
In the camera contained such an active distance measurement system, when a shutter release button is half depressed, a power source voltage check and an external luminance measurement are carried out. Then, the distance measurement system starts a distance measurement. Subsequently, the shutter release button is fully depressed, it allows a shutter to open for a certain period of time for exposure film to light.